In digital data communications there are known several internationally standardized systems and network implementations based on them. A user of a data communication service is usually not interested in the technical details of the system or network that conveys his or her message. From the user's point of view user-friendliness means that various networks and systems can be made to work together in a versatile and reliable way, thus making it possible to use a variety of services from a terminal of any one system. In the description below we will use the GSM and DECT systems as examples.
The data communication services of both the GSM (Groupe Speciale Mobile/Global System for Mobile Communications) system and the DECT (Digital European Cordless Telecommunications) system are widely used in Europe. In both systems the principle is the same: the user has a small and lightweight portable terminal which for data communication purposes is radio-linked to a fixed base station which in turn is linked in a fixed manner to a switching centre equipment controlling the operation of the system. The systems employ different standardized functions for packetizing, encoding and modulating the data to be transferred. Data is handled according to so-called protocols, which are known to those skilled in the art. The GSM system protocols relevant to this invention and instructions for their implementation are described e.g. in the "The GSM System for Mobile Communications" by Michel Mouly and Marie-Bernadette Pautet, published by the authors, ISBN 2-9507190-0-7, Palaiseau 1992, 701 pp. The DECT system protocols relevant to this invention and instructions for their implementation are described e.g. in the following standards and documents: ETS 300 175-1 to 300 175-8, prETS 300 444, prETS 300 331, I-ETS 300 176, ETR 015, ETR 043, ETR 056, prETS 300 466, ETS 300 370 and ETS 300 xxx: "Radio Equipment and Systems (RES); Digital European Cordless Telecommunications (DECT) Data services profile, Generic data link service, Service Type C, Class 2".
It is known to connect a DECT base station, called a fixed part (FP), directly to a GSM mobile switching centre (MSC), thus making it possible to have a speech connection from a mobile telephone in a DECT system to another telephone through a GSM network. The methods so far have not, however, provided the possibility of using the varied range of GSM system data services during such a connection since there has not been a method of implementing the rate adaptations required by these services in the data communication between the systems.